Isolator



1970 J. F. WORTHINGTON 3,539,961

ISOLATOR Filed April 11; 1969 United States Patent US. Cl. 337-197 Claims ABSTRACT OF THE DISCLOSURE The isolator is designed to protect electrical appliances from electrical current in excess of a predetermined value. The device which is plugged by means of a male plug member into an ordinary three prong grounded wall receptacle has a female receptacle for receiving the prongs of a plug connected to an appliance. The male plug member and the female receptacle are electrically interconnected by fusible wire. An arc plate, connected to a third prong, is disposed adjacent the male prong members of the isolator so when current in excess of a predetermined value flows through the device the fuse wire is burned out and the current is carried by the arc plate to ground thereby effectively isolating the appliance and saving it from damage.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an electrical isolator and more particularly to an isolator for isolating electrical appliances and the like from electrical currents in excess of a predetermined value.

Description of the prior art current overload which might be less than that required to open the circuit breaker or burn out a fuse might still be great enough to damage the appliance. Typically these current overloads result from voltage surges caused by lightning striking the structure in which these appliances are housed, or by striking an exposed power line.

SUMMARY OF THE INVENTION Generally, this invention relates to a device for isolating an electrical appliance from an electrical current in excess of a predetermined value. The device comprises a housing which supports a plurality of prong means adapted to be inserted in a grounded electrical receptacle, and a female receptacle adapted to be electrically connected to an appliance. Fusible means are connected between at least two of the prong means and the female receptacle. The fusible means are adapted to electrically disconnect the two prong means from the female receptacle when it carries an electrical current whose value is greater than a predetermined value. Are means are disposed in the housing adjacent the two prong means and are spaced slightly therefrom to define a spark gap. The arc means is connected to another of the prong means so that when the two prong means and the electrical receptacle are electrically disconnected current in the two prong means is conducted to said other prong means by way of said spark gap and said arc means.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings FIG. 1 is a pictorial illustration of an isolator constructed according to the invention installed 3,539,951 Patented Nov. 10, 1970 ice in a wall receptacle and having an electrical appliance connected to it;

FIG. 2 is a front elevational view of the isolator of FIG. 1;

FIG. 3 is a rear elevational view of the isolator of FIG. 1;

FIG. 4 is a sectional view of the isolator taken along line 4-4 of FIG. 2;

FIG. 5 is a sectional view of the isolator taken along line 5-5 of FIG. 4;

FIG. 6 is a sectional view of the isolator taken along line 6-6 of FIG. 4; and

FIG. 7 is a view of the isolator taken along line 7-7 of FIG. 5.

BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings for a detailed description of the invention, FIG. 1 shows a typical electrical appliance such as a television set 12 with an electrical power cord 14 having a plug 16 connected to an isolator 20 constructed in accordance with a preferred form of the invention. The isolator 20 is plugged into an ordinary three prong wall receptacle in a manner which will be explained herein.

With reference to FIGS. 2 and 3 it can be seen that the isolator 20 is designed so that it fits entirely within a housing 22 which is preferably made of a high impact plastic material. The only externally visible parts of the device are two male prong members 24 and a ground prong 27 which extend from one side of the housing and on its opposite side are a female receptacle 28 and an indicator lamp 30.

A preferred construction of the housing 22 is shown in FIG. 4. The housing comprises a back member 32 defining a rear wall and a cup-like member 34 which forms the top and bottom walls 35 and 36, the side walls 37 and the front 38 of the housing. The cup-like member 34 can be snapped into place over ribs 33 on rear Wall member 32 or if desired can be connected thereto by suitable screws as is well known in the art.

The male prong members 24 comprise two prongs 25 and 26. Each prong may be fastened to the rear wall 32 of housing 22 by a suitable anchor member 40 which is imbedded in the wall. Extending rearwardly from each anchor member 40 is an electrode 41, 42. Preferably, the electrodes are substantially the same size as the prongs 25 and 26 and may be integrally connected thereto.

Each electrode 41 ad 42 is in air chamber 46 formed by a suitable hollow member such as tube 48 which may be made a suitable nonconductive material such as a plastic or glass. The tubes 48 are supported on rear wall 32 by bosses 50 projecting into the housing so that the tubes extend slightly beyond the ends of the electrodes.

Disposed below prongs 25 and 26 is the aforementioned centrally located ground prong 27 which is secured to the rear Wall 32 by a suitable anchor element 53. A portion 55 of the ground prong extends rearwardly into the housing to support an arc plate 57 which has a rectangular upper portion in opposed relation to electrodes 41 and 42 and a lower portion that tapers to its juncture 60 with the rearwardly extending portion 55 of prong 27.

As best seen in FIGS. 4 and 6 the arc plate 57, which may be made from copper, is held against the free ends 59 of the tubes 48 so that spark gaps 61 and 62 between the plate and the ends of the electrodes can be accurately determined. As is well known the size of these gaps will be determinative of the voltage value at which a spark will be able to reach the arc plate from the electrodes.

:In FIGS. 4 and 7 female receptacle 28 includes two recesses 64 and 65 which are formed on a ledge 66 projecting inwardly from the front wall 38 of the housing 3 and which have installed therein electrically conductive blades 67 and 68. Each of the blades is secured in its respective recess by suitable fasteners such as rivets or screws 70 which connect legs 71 and 72 on each of the blades to the ledge 66.

Electrode 41 is connected to blade 67 and electrode 42 is connected to blade 68 by fuse wires 73 and 74. In this regard it is to be observed that the ends of fuse wires 73 and 74 pass through tubes 48 and are connected within the air chambers 46 to ends of the electrodes nearest arc plate 57. As is well known in the art, the size and the material from which the wire is made will determine the maximum value at which the fuse will burn out to disconnect the receptacle.

Indicator lamp 30 is located in a socket 76 formed in the front wall 38 of the housing. As illustrated in FIGS. 4 and 5 the lamp is connected across the blades of the female receptacle so that when voltage is available between the blades, it will glow. The lamp socket 76 is connected to one leg 71 by a wire 78 having a resistor 80 located therein. The base of the receptacle is connected to the other leg 72 by a second wire 82.

Referring now to the mode of operation of the isolator, male prong members 24 and ground prong 27 plug into an ordinary three prong wall receptacle so that prongs 25 and 26 form a part of the electric circuit and prong 27 is grounded. As long as the fuse wires 73 and 74 are intact indicator lamp draws a small current through prong 25, electrode 41, fuse wire 73, leg 71, wire 78 and resistor 80 to the lamp. The return circuit is through wire- 82 to leg 72, fuse. wire 74, electrode 42 and return prong 26. When an appliance is plugged into the female receptacle 28 the loadon the fuse wires ,73 and 74 increases substantially, however, as long as it is below the predetermined value the wires remain intact. Since the lamp offers much less resistance to the current than the appliance,resistorv 80 has a-relatively high value to assure that the current will be shunted to the appliance rather than to the lamp. In the event a current overload which might be caused by lightning, enters the line the portion of the fuse wires 73 and 74 inside air chamber 46 will burn out opening the circuit between prong members 24 and the appliance and extinguishing the indicator lamp.

The high voltage in the line will cause a spark to leap the gap 61 and 62 between each electrode 41 and 42 and are plate 57 whereupon the current will be conducted by projection 55 to prong 27 and then into the grounded receptacle thereby effectively isolating the appliance.

While the isolator has been described with reference to an embodiment having a female receptacle with two blades and a male plug member with two electrically conductive prongs and a ground prong, the invention can also be practiced in embodiments where the female receptacle has more than two blades and the male plug member has more than three prongs if additional fuse wires and electrodes are provided.

While the isolator device has been described with reference to a particular embodiment thereof which has been described andillustrated herein, it is to be understood that the description of the preferred embodiment is intended to be merely illustrative and thus the scope of the invention should not be limited thereby since many obvious modifications of this embodiment will be ap-v parent to those skilled in the art. Accordingly, the scope of the invention should only be defined in accordance with the claims appended hereto.

What is claimed is:

1. A device for isolating an electrical appliance operating at the current and voltage levels normally used with household appliances from an electric current in excess of a predetermined value comprising:

a housing supporting a plurality of prong means adapted to 'be inserted into a grounded electrical receptacle and a female receptacle adapted to be electrically connected to an appliance;

a plurality of electrode means connected, respectively, to each said prong means and extending inwardly of said housing;

fusible means connected between at least two of said electrode rmeans and said female receptacle, said fusible means being adapted to electrically disconnect said two electrode means and said female receptacle when said fusible means are caused to carry an electric current in excess of a predetermined value;

hollow means defining an air chamber surrounding said electrode means, said hollow means being supported by portion of said housing means and being closed at one end by said portion of said housing and open at the end adjacent the ends of said electrode means remote from said prong means, said connection between said fusible means and said electrode means being within said air chamber; and

arc means disposed in said housing adjacent to the ends of said two electrode means remote from said prong means and spaced therefrom to define a spark gap, said are means being electrically connected to another of said prong means so that when said two electrode means and said receptacle are electrically disconnected, current in said two prong means is conducted to said other prong means by way of said-spark gap and said arc means;

2. A device as defined in claim 8 wherein said fusible means are 'conected'to said prong means at the end of each electrode adjacent said are means.

3. A device as defined in claim 4 wherein said female receptacle comprises at least two blades and said fusible means includes at least two fuse wires; and

each of said wires connects one of said blades to one of said electrodes.

4. A device as defined in claim 4 wherein said are means includes an electrically conductive plate.

5. A device as defined in claim 5 including:

a lamp electrically connected across said blades, said lamp being operative until said fusible means carries an electric current in excess of said predetermined value.

References Cited UNITED STATES PATENTS 606,771 7/1898 Smith 337199 2,988,617 7 6/1961 Graziosi 337l99 XR 3,256,408 6/1966 Stumpe et al. 337273 BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner US. Cl. X.R. 337282 

